[etherlab-users] delays in the etherlab I/O blocks?

[Julian Stoev / Юлиан Стоев]

On Mon, Oct 19, 2009 at 5:13 PM, Florian Pose <fp at igh-essen.com> wrote:
> On Mon, Oct 19, 2009 at 03:19:36PM +0200, Julian Stoev /  Юлиан Стоев wrote:
>>
>> I am not sure I understand exactly. Do you mean that querying and
>> actual reading of the slaves should be regarded as two different
>> samples. The command is given to query. The values become available on
>> the next time sample?
>
> It just means, that if you send a command to a slave at cycle n, the
> response to this command is visible in the process data in cycle n + 2,
> because reading and writing is done together at the beginning of each
> cycle.
>

Then again, if I understand correctly, the values should be available
at n+1, not n+2?

But I think the n+2 is exactly as we detected it.
When the loop was working at uniform 1kHz there was a delay ~3ms => 1
ms input delay due to sampling + 2 ms output delays. This is the
correct math?

This would indicate two options:
1. One has benefit to always run the I/O blocks at the maximum
possible sampling rate to minimize such delays.
2. One can make a double quick sample to get minimum output delay and
then wait for the normal "long" sampling rate.  Such is the approach
for example in ADC in hard disk drive firmware.

>From Simulink point of view the first option is more simple perhaps,
but has slight overhead.


-- 
Julian Stoev, PhD.
Control Researcher